Graft copolymers of an alkenyl-substituted aromatic compound, and unsaturated ester and a preformed copolymer of an alkenyl-substituted aromatic compound and a polyolefin



United States Patent GRAFT COPOLYMERS OF AN ALKENYL-SUBSTI- TUTEDAROMATIC COMPOUND, AND UNSAT- URATED ESTER AND A PREFORNIED COPOLY- MEROF AN ALKENYL-SUBSTITUTED ARO- MATIC COMPOUND AND A POLYOLEFIN HenryGeorge Hammon, Columbus, Richard A. Clark, Worthington, and John W.Uttley, Jr., Hilliards, Ohio, assignors, by mesne assignments, to ShellOil Company, Emeryville, Calif., a corporation of Delaware No Drawing.Filed Oct. 29, 1958, Ser. No. 770,254

15 Claims. (Cl. 260-455) This invention relates to new polymericproducts and to a method for their preparation. More particularly, theinvention relates to a new class of graft copolymers prepared fromalkenyl-substituted aromatic compounds which have improved clarity andunusually high impact strength.

Specifically, the invention provides new and particularly useful graftcopolymers comprising the product of polymerization of (1) analkenyl-substituted aromatic compound, (2) an ethylenically unsaturatedester, and (3) a preformed copolymer of an alkenyl-substituted aromaticcompound and a polyolefin.

Conventional styrene homopolymers and copolymers are useful as moldingresins, but do not exhibit sufiicient impact strength for a great manyapplications. Some conventional clear resins containing styrene mayexhibit somewhat higher impact strengths. However, these resins usuallyare soft, have low heat distortion temperatures, and only obtainimproved impact strength by sacrificing other useful properties.

Because of the ready availability of styrene and substituted styrenes atfavorable prices, a need exists in the art for clear, high-impactstrength, styrene molding resins based on polystyrenes, or conventionalcopolymers and terpolymers containing a styrene. Impact strengthcommonly obtained with polystyrene and its coor terpolymers is in theorder of 0.2 to 0.5 ft./lb./in., notch. Clear styrene-base polymershaving excellent molding properties and having impact strengths greaterthan 0.5 ft./lb./in., would constitute a significant improvement in theart.

It is, therefore, an object of the invention to provide a superiormolding resin. it is a further object to provide molding resins havingsuperior impact strength. It is a further object to provide a highimpact molding resin having improved clarity. It is a further object toprovide a new high impact strength resin which is hard and has good heatresistance. These and other objects of the invention will be apparentfrom the following detailed description thereof.

It has now been discovered that these and other objects may beaccomplished by the new graft copolymers of the invention comprising theproduct of polymerization of (1) an alkenyl-substituted aromaticcompound, (2) an ethylenically unsaturated ester, and (3) a preformedcopolymer of an alkenyl-substituted aromatic compound and a polyolefin.It has been found that these special graft copolymers have unexpectedlysuperior properties, particularly as to clarity and impact strength. Thenew graft copolymers, for example, have impact strengths above those ofconventional polystyrene and have impact strengths which, in many cases,go as high or higher than 1.10 ft./lbs./in., notch. Surprisingly, thesesuperior properties, such as clarity and improved impact strength, areobtained without any sacrifice in the other desired properties, such ashardness and good heat resistance.

The new copolymers of the invention are to be distinguished in structurefrom the conventional copolymers and terpolymers formed by polymerizingan initial mixture containing the monomers, such as the above-noted icealkenyl-substituted aromatic compounds, unsaturated esters andpolyolefins. In such a conventional process, the resulting polymers havea random mixture of the three monomer units all along the polymerbackbone chain. The new copolymers of the invention, however, have agraft structure wherein the alkenyl-substituted aromatic compound andpolyolefin units make up the polymer backbone chain and polymer chainsof the alkenyl-substituted aromatic compounds and unsaturated esterunits are attached (grafted) at random along the side of the saidpolymer backbone chain. Such a structure is unique in that the backbonepolymer retains its original structure and the modification is in thegraft sidechains instead of the backbone polymer itself. For claritythroughout the specification and claims, the initial preformed polymerused in making the graft copolymers may be referred to as the backbonepolymer and the monomers used in making the graft polymer chains will bereferred to as the grafting monomers.

The preformed polymer used as the backbone polymer in the preparation ofthe new graft copolymers of the present invention comprises the productof polymerization of an alkenyl-substituted aromatic compound and apolyolefin. The alkenyl-substituted aromatic compounds include thosecompounds having an alkenyl group, and preferably a l-alkenyl group,e.g., a vinyl group, attached to a ring carbon atom of an aromatic ring.Examples of these include, among others, styrene, alpha-methylstyrene,vinyl toluene, 2-chlorostyrene, 4- chlorostyrene, 2,4-dichlorostyrene,2,5-dichlorostyrene, vinyl naphthalene, Z-methylstyrene,2,4-diethylstyrene, 2,3,4-trimethylstyrene, 2,4-diisobutylstyrene,3-tert-butylstyrene, 4-octylstyrene, allylstyrene, 4-cyclohexylstyrene,and the like, and mixtures thereof. Preferred alkenylsubstitutedaromatic compounds include the styrenes, such as styrene itself and thehalo-substituted styrenes and styrenes substituted with a hydrocarbonradical, the substituents being on the vinyl side chain or on thearomatic ring. Particularly preferred are styrene, alpha-alkylstyrenesand the monoand dichloroand monoand polyalkyl-substituted styreneswherein the substituents are attached to ring carbon atoms, saidsubstituted styrenes containing up to 12 carbon atoms. Corning underspecial consideration, particularly because of the superior propertiesof the resulting products as well as the ready available and low cost isstyrene itself.

A minor portion, e.g. up to 10% by weight, of the alkenyl-substitutedaromatic compound can be replaced with any \of the hereinbelow describedunsaturated esters.

The polyolefins used in the preparation of the preformed polymerscomprising the conjugated open-chained dienes. Examples of suchconjugated dienes include, among others, butadiene-l,3, isoprene,2,3-dimethylbutadiene, pentadiene-l,3, methylpentadiene, and the like,and mixtures thereof. As the number of carbon atoms in the polyolefin isincreased above eight, a decline in the favorable properties of thegraft copolymer generally result. Remarkably superior results areobtained, however, when the diene contains 5 to 7 carbon atoms. Bestresults are obtained when the diene is isoprene.

The amount of the conjugated polyolefin in the finished preformedpolymer may vary within certain limits. The amount of the polyolefin issmall and should generally not be above 10 parts per parts of thepreformed polymer. Preferably, the polyolefin should be between .5 to 2parts by weight and the alkenyl-substituted aro matic compound from 99.5to 98 parts by weight.

The preformed polymers of the alkenyl-substituted aromatic compound andthe polyolefins can be prepared by any suitable method. They may beprepared, for example, by polymerization in solution or in aqueous emu]sion or suspension systems. The aqueous emulsion technique was found togive highly superior products and is the more preferred. In this case,the preformed polymers are preferably prepared by heating the monomerstogether in an aqueous emulsion in the presence of a free radicalyielding catalyst. Examples of the preferred catalysts include, amongothers, per-acids as persulfuric acid, salts of peracids as ammoniumpersulfate, potassium persulfate, peroxides as benzoyl peroxide,hydrogen peroxide, di-tertiary butyl peroxide, di-tert-butyl succinate,tertbutyl peracetate, di-tert-butyl dipermalonate, and 2,2-bis(tert-butylperoxy)butane. The amount of the catalyst employed ispreferably between 0.05% to 5% by weight of the monomers to bepolymerized, and still more preferably between 0.1% and 1.0% by weightthereof.

Any of the known emulsifying agents may be employed. These includeparticularly the ionic surface active agents, especially those having apolar structure including a hydrophilic (predominantly hydrocarbon)residue and a charged (ionic) radical thereon, such as anionicsurfaceactive compounds including alkali metal and nitrogenbase soaps ofhigher fatty acids, such as potassium and/ or sodium myristate, laurate,palmitate, oleate, stearate, ammonium stearate, etc., as well as thesurface-active compounds of the cation-active variety, such as salts oflong-chain aliphatic amines and quaternary ammonium bases, such aslauryl amine hydrochloride, stearyl amine, hydrochloride, and palmitylamine hydrobromide. Additional examples of suitable ionic surface-activeemulsifying agents include the alkali metal or ammonium alkyl oralkylene sulfates or sulfonates, such as sodium and/ or potassium laurylsulfate, alkyl, aryl and alkylated aryl sulfonates, cetyl sulfonate,oleyl sulfonate, stearyl sulfonate, sulfonated Turkey red oil,sulfonated mineral oils, sodium, potassium and ammonium isopropylnaphthalene sulfonate, amine soaps, such as triethanolamine stearate,amino-substituted alcohols, sulfonated fatty esters and amides, thehydrochloride of diethyl aminoethyloleylamide, trimethylcetyl ammoniummethyl sulfate, alkenesulfonic acids, alkali metal and ammonium salts ofsulphonated long-chain hydrocarbons, or sulphonated longchain fattyacids, such as sulphonated oleic acid and the sodium, potassium andammonium salts of sulphated cetyl alcohol. Starch, gum-arabic, thepolyoxyalkylene oxide condensates of hexitan anhydrides,carboxymethylcellulose, etc. may also be used.

In the event products are desired which have outstanding clarity oneshould employ emulsifying agents such as tetrasodium-N- 1,2-dicarboxyethyl) -N-octadecylsuliosuccinamate, which is commerciallyavailable under the name of Aerosol 22 as a 35 percent active solution,sodium dodecylbenzene sulfonate, which is commercially available underthe trade name of Ultrawet 30, and decylbenzene sodium sulfonate, whichis available under the trade name of Santomerse S. Especially preferredis Aerosol 22.

The emulsifying agents are preferably employed in amounts varying fromabout 0.1% to 5% by weight of the monomers to be polymerized.

The reaction is preferably conducted in an inert atmosphere, such asnitrogen, methane and the like.

Temperatures employed in the formation of the preformed backbonecopolymer will vary depending upon the catalyst selected. Preferredtemperatures range from about 40 C. to about 150 C. Particularlypreferred temperatures range from about 40 C. to 80 C. Superatmospheric,atmospheric or subatmospheric pressures may be used as desired.

The above-described backbone polymer should be retained in the originalpolymerization mixture, such as the aqueous latex, for the subsequentgrafting operation.

The monomers to be copolymerized with the above described backbonepolymer comprising the alkenyl-substituted aromatic compounds and theethylenically unsaturated esters. The alkenyl-substituted aromaticcompounds employed may be any of those described above fumarate, dibutylS-butenedioate acid and the like. Also for the preparation of thebackbone copolymer, such as, for example, styrene, alpha-methylstyrene,vinyl toluene, 2 chlorostyrene, 4 chlorostyrene, 2,4 dichlorostyrene,vinylnaphthalene, Z-methylstyrene, 2,4-diethylstyrene,2,3,4-trimethylstyrene, 4-cyclohexylstyrene, and the like, and mixturesthereof. The alkenyl-substituted aromatic compound selected preferablyis, but need not be, the same as the alkenyl-substituted aromaticcompound used in the preparation of the backbone copolymer. Particularlypreferred alkenyl-substituted aromatic compounds include the styrenes,such as styrene itself and the halosubstituted styrenes and styrenessubstituted with a hydrocarbon radical wherein the substituent is placedon the vinyl side chain or the aromatic ring. Especially preferred arethe above-noted styrenes containing no more than 12 carbon atoms.

The unsaturated ester to be used in preparing the new graft copolymerscomprise the monomeric organic esters possessing at least one group andat least one carbon-to-carbon unsaturated linkage as an ethyleniclinkage. A preferred group of the unsaturated esters comprise the estersof ethylenically unsaturated monocarboxylic acids and monohydricalcohols. Examples of this group comprise, among others, methylmethacrylate, ethyl methacrylate, butyl methacrylate, ethyl acrylate,isopropyl acrylate, cyclohexyl acrylate, allyl acrylate, allylmethacrylate, octyl acrylate, octenyl methacrylate, butyl crotonate,cyclohexyl crotonate, and the like. Another preferred group ofunsaturated esters comprise the esters of ethylenically unsaturatedmonocarboxylic acids and polyhydric alcohols, such as, for example,ethylene glycol diacrylate, ethylene glycol dimethacrylate, butyleneglycol dicrotonate, hexylene glycol diacrylate, ethylene glycolacrylate, methacrylate and cyclohexenediol diacrylate. Another preferredgroup comprise the esters of saturated aliphatic or cycloaliphaticmonohydric alcohols and unsaturated polycarboxylic acids, such as, forexample, diethyl maleate, dibutyl useful, but less preferred are theesters of ethylenically unsaturated alcohols and monocarboxylic acids,such as allyl acetate, allyl butyrate, allyl propionate, allylcyclohexane-carboxylate and the like.

Especially preferred are the esters of the ethylenically unsaturatedaliphatic and cycloaliphatic monocarboxylic acids containing from 3 to10 carbon atoms and the saturated aliphatic and cycloaliphaticmonohydric alcohols containing from 1 to 10 carbon atoms, and the estersof the aforedescribed monocarboxylic acids and saturated aliphatic andcycloaliphatic diand trihydric alcohols containing from 2 to 10 carbonatoms. Particularly superior results are obtained when the unsaturatedester contains from 8 to 12 carbon atoms. Ethyl acrylate is especiallypreferred.

The ratio in which the alkenyl-substituted aromatic compounds and theunsaturated ester are used in preparing the graft copolymer may varywithin certain limits. The alkenyl-substituted aromatic compound and theunsaturated ester may be employed in ratios varying from 2.5 :1 to 4:1.The best properties in the graft polymer are obtained when the ratio ofthe alkenyl-substituted aromatic compounds to the ester is about 3:1.

The total amount of the grafting monomers to be used in preparing thenew graft copolymers will vary from about 40 to 70 parts of suchmonomers to 60 to 30 parts of the above-described backbone polymer. In apreferred embodiment of the invention, the grafting monomers constituteabout 60 parts by weight and the backbone copolymer comprises about 40parts by weight. In such a preferred embodiment, the polyolefin ispresent in only relatively small proportions, e.g. not more than about 1part by weight. However, the presence of a relatively small amount ofthe diene in the backbone of the copolymer and consequently present inthe final graft copolymer yields unexpectedly superior impart strength.

The graft copolymer of the invention are prepared by adding theabove-described grafting monomers to the polymerization mediumcontaining the preformed polymer and then continuing the polymerization.In the preferred procedure, the desired monomers are added all at onceor in small increments to the medium containing the above-describedpreformed polymer and the mixture then heated in an inert atmosphere.

In some cases, it may be desirable to add additional free radicalyielding catalysts, such as those described above to speed the formationof the graft. Such catalysts are generally added in amounts varying fromabout 0.1% to 4% by weight.

Additional emulsifying agent may also be added. Particularly preferredagents include tetrasodium-N-(l,2- dicarboxyethyl) Noctadecylsulfosuccinamate, sodium dodecyl benzene sulfonate, anddecylbenzene sodium sulfonate. Especially preferred is theabove-described Aerosol 22. Such agents are preferably employed inamounts varying from about .5% to 5% by weight of the monomer andpolymer being polymerized. The monomers may be added all at one time orone or more of the monomers may be added in small increments orcontinuously throughout the reaction.

Temperatures employed in the formation of the graft will vary dependingupon the rate desired, catalyst selected and the like. Preferredtemperatures range from about 40 C. to about 150 C. The rate of graftinggenerally goes up as the temperature is increased. Particularlypreferred temperatures to be used with the conventional free radicalyielding catalysts range from about 40 C. to about 80 C.Superatmospheric, atmospheric or subatmospheric pressures may be used asdesired.

The grafting process is accomplished in the absence of molecular oxygen.This is preferably accomplished by conducting the reaction in thepresence of an inert gas, such as nitrogen, methane and the like.

At the conclusion of the reaction, i.e. when substantially all of themonomer has been consumed, the graft copolymer can be recovered from thereaction mixture by any suitable method such as freezing, precipitation,extraction, filtration and the like. In the case of aqueous emulsionssystems, the copolymer is preferably removed by freezing and thawing orby coagulation with alcohols and the like.

The graft copolymers prepared by the above process are soft to hardsolids having molecular weights ranging from about 5,000 to about150,000 as determined by the light scattering technique as described inChem. Rev., vol. 40, page 319 (1940). The copolymers may be molded inconventional injection and compression molding techniques to formvaluable molded articles. The copolymers are particularly suited for usein preparing articles, such as drinking tumblers, dishes, and foodcovers and the like. They should also prove useful in lens systems Wherethe optical requirements are not stringent, for example, in tail lightcovers on automobiles. Other uses will be obvious to those skilled inthe art.

The following examples more specifically describe a preferred manner inwhich the invention may be practiced and illustrated certain of itsadvantages and the benefits to be obtained therefrom. In the examplesall parts are by weight, and impact strengths are in footpounds, perinch, notch, determined in accordance with ASTM D25654T, Az-inch bar.

Example I A heavy-walled glass container was used as the reaction vesselfor the polymerization. A water solution of tetrasodium N (1,2dicarboxyethyl) N octadecylsulfosuccinamate, was prepared, containing1.5 of

Ingredients Water Tetrasodium-N-( 1,2-dicarboxyethyl)- Parts by weightN-octadecylsulfosuccinamate 1.5 Ammonium persulfate 1 Tertiary-dodecylmercaptan 0.1 Styrene 39.5 Isoprene 0.5

Air was removed from the container by purging with nitrogen. Thecontainer was closed with a self-sealing cap, and the container was thenplaced in a rack and rotated end-over-end in a thermostaticallycontrolled water bath set at 50 C. The reaction was run to completion inabout three hours. The copolymer so formed serves as the base polymer,or backbone, for formation of the graft polymer.

For the grafting portion of the polymerization, 45 parts by Weight ofstyrene and 15 parts by weight of ethyl acrylate were added to thereaction chamber containing the backbone copolymer. The reaction vesselwas then replaced in the water bath and polymerization allowed tocontinue at 50 C. The polymer was coagulated by freezing and thawing andfiltering.

The graft polymer formed was a clear solid exhibiting an impact strengthof 0.72.

Example II Following the procedure of Example I, 45 parts of styrene and15 parts of ethylacrylate were grafted upon a copolymer backboneconsisting essentially of 39.88 parts of styrene and 0.20 part ofisoprene. The polymerization temperature was 55 C. The graft polymerthus prepared was clear and exhibited an impact strength of 0.57.

Example 111 Following the procedure of Example I, 45 parts of styreneand 15 parts of ethyl acrylate were grafted upon a copolymer backboneconsisting essentially of 39.96 parts of styrene and 0.04 part ofisoprene. The polymerization temperature was 55 C. This polymerexhibited a somewhat lower impact strength and was less clear.

Example IV A copolymer backbone, containing 57.6 parts of styrene and2.4 parts of butadiene, was polymerized at 65 C.; 1.5 parts oftetrasodium-N-(1,2-dicarboxyethyl) N-octadecylsulfosuccinamate were usedas the emulsifier. Next, 30 parts of styrene and 10 parts of ethylacrylate were grafted upon the copolymer backbone. A graft polymer wasthus prepared, which exhibited an impact strength of 0.43.

Example V A copolymer backbone, consisting essentially of 54 parts ofstyrene, 5.9 parts of ethyl acrylate, and 0.1 part of isoprene waspolymerized at 50 C. A graft of 30 parts of styrene and 10 parts ofethyl acrylate was then polymerized with the backbone, forming a cleargraft polymer. The impact strength of this polymer was 0.61.

Example VI Using emulsion-polymerization techniques, a backboneterpolymer of 53 parts of styrene, 6 parts of ethyl acrylate, and 6parts of isoprene was polymerized at 50 C. A mixture of 25 parts ofstyrene and 10 parts of ethyl acrylate was then grafted upon thecopolymer backbone. The clear graft polymer thus prepared had an impactstrength of 0.61.

Example VII If methyl styrene, ethyl styrene, dimethyl styrene, ormixtures thereof are used in place of all, or part, of this styrene inthe preceding examples, there will be obtained graft polymers havingimpact strengths equal, or superior, to conventional polystyrenes.

Example VIII If methyl acrylate, ethyl methacrylate, methylmethacrylate, or mixtures thereof, are used in place of all, or part ofthe ethyl acrylate in the grafting portion of the polymers of thepreceding examples, there will be obtained graft polymers having impactstrengths equal, or superior, to conventional polystyrenes.

Example IX Using the emulsion-polymerization technique, 38 parts ofstyrene and 1.9 parts of isoprene were polymerized. A mixture of 45parts of styrene and 15 parts of ethyl acrylate were then grafted uponthe copolymer previously formed. The clear graft polymer producedexhibited an impact strength of 1.10.

Example X Using emulsion-polymerization techniques, a copolymerconsisting essentially of 54 parts of styrene and 6 parts of ethylacrylate was prepared. A mixture of 28 parts of styrene and 12 parts ofethyl acrylate were grafted upon this copolymer. A graft polymerresulted, which exhibited an impact strength of 0.35.

It is to be noted that Example X is not intended to be illustrative ofpolymers prepared by this invention. Rather, it is intended toillustrate the novel and important effect of the addition of aconjugated diene, such as isoprene, to the graft polymer. It can readilybe seen that the absence of the conjugated diene results in a reducedimpact strength in the resulting polymer.

It is obvious from the above description and examples that manymodifications can be made without departing from the spirit and scope ofthe invention. It is intended that all such modifications should beincluded hereunder.

We claim as our invention:

1. A graft copolymer composition comprising the product ofpolymerization of a mixture of (1) 40 to 70 parts by weight of a mixtureof monomers comprising styrene and an alkyl ester of an ethylenicallyunsaturated monocarboxylic acid containing up to 12 carbon atoms, and(2) 60 to 30 parts by weight of a copolymer of styrene and a conjugateddiene containing 4 to 8 carbon atoms, which copolymer contains no 'morethan 10 parts per 100 parts of copolymer of polymerized conjugateddiene.

' 2. The graft copolymer composition of claim 1 where the alkyl ester ofan ethylenically unsaturated monocarboxylic acid is ethyl acrylate.

3. The graft copolymer composition of claim 1 Wherein the conjugateddiene used in making the copolymer is isoprene.

4. A graft copolymer composition comprising the product ofpolymerization of a mixture of (1) 40 to 70 parts by weight of a mixtureof monomers comprising styrene and an'unsaturated monocarboxylic acidester containing up to 12 carbon atoms wherein the styrene andunsaturated ester are employed in a weight ratio of 2.5 :1 to 4:1, and(2) 60 to 30 parts by Weight of a preformed copolymer of styrene and aconjugated diene containing 4 to 8 carbon atoms, the said preformedcopolymer containing not more than 10 parts per 100 parts of copolymerof polymerized conjugated diene.

5. The graft copolymer composition of claim 4 where the unsaturatedester is ethylene glycol diacrylate.

6. The graft copolymer composition of claim 4 where the unsaturatedester is methyl methacrylate.

7. A graft copolymer composition comprising the product ofpolymerization of a mixture of (l) 60 parts of a mixture of styrene andethyl acrylate and (2) 40 parts of a preformed copolymer of styrene anda conjugated diene containing 5 to 7 carbon atoms, said preformedcopolymer containing not more than 10 parts per 100 parts of copolymerof polymerized conjugated diene.

8. The graft copolymer composition of claim 7 where the polymerizedconjugated diene comprises about 0.1 to 2.0 parts by weight of thepreformed copolymer.

9. The graft copolymer composition of claim 7 Where the polymerizedconjugated diene comprises about 0.5 part by weight of the preformedcopolymer.

10. A graft copolymer composition comprising the product ofpolymerization of a mixture of (1) about 45 parts by weight of styrene,(2) about 15 parts by weight of ethyl acrylate, and (3) 40 parts of acopolymer backbone of about 39.5 p rts by weight of styrene and about0.5 part by weight tgpisoprene.

11. A graft cop ymer composition comprising the product ofpolymerization of a mixture of 1) about 54 parts by weight of styrene,(2) 5.9 parts by weight of ethyl acrylate, and 0.1 part by weight ofethylene diacrylate, and (3) 40 parts of a copolymer of about 39.5 partsby weight of styrene and about 0.5 part by weight of isoprene.

12. A graft copolymer composition comprising the product ofpolymerization of a mixture of (1) 40 to parts by Weight of a mixture ofan alkenyl-substituted aromatic compound selected from the groupconsisting of styrene, alpha-alkylstyrenes and the monoand dichloroandmonoand polyalkyl-substituted styrenes wherein the substituents areattached to ring carbon atoms, said substituted styrenes containing upto 12 carbon atoms, and an ethylenically unsaturated monocarboxylic acidester containing up to 12 carbon atoms, and (2) 60 to 30 parts by weightof a preformed copolymer of 99.5 to parts by Weight of analkenyl-substituted aromatic compound hereinbefore described and 0.5 to10 parts by Weight of a conjugated diene containing from 4 to 8 carbonatoms.

13. A graft copolymer as in claim 12 wherein the alkenyl-substitutedaromatic compound in the mixture of monomers and in the preformedcopolymer is styrene.

14. A graft copolymer composition as in claim 12 wherein the conjugateddiene is isoprene.

15. A graft copolymer composition as in claim 12 wherein the ester isethyl acrylate.

References Cited in the file of this patent UNITED STATES PATENTS

12. A GRAFT COPOLYMER COMPOSITION COMPRISING THE PRODUCT OFPOLYMERIZATION OF A MIXTURE OF (1) 40 TO 70 PARTS BY WEIGHT OF A MIXTUREOF AN ALKENYL-SUBSTITUTED AROMATIC COMPOUND SELECTED FROM THE GROUPCONSISTING OF STYRENE, ALPHA-ALKYLSTYRENES AND THE MONO- AND DICHLOROANDMONO- AND POLYALKYL-SUBSTITUTED STYRENES WHEREIN THE SUBSTITUENTS AREATTACHED TO RING CARBON ATOMS, SAID SUBSTITUTED STYRENES CONTAINING UPTO 12 CARBON ATOMS, AND AN ETHYLENICALLY UNSATURATED MONOCARBOXYLIC ACIDESTER CONTAINING UP TO 12 CARBON ATOMS, AND (2) 60 TO 30 PARTS BY WEIGHTOF A PREFORMED COPOLYMER OF 99.5 TO 90 PARTS BY WEIGHT OF ANALKENYL-SUBSTITUTED AROMATIC COMPOUND HEREINBEFORE DESCRIBED AND 0.5 TO10 PARTS BY WEIGHT OF A CONJUGATED DIENE CONTAINING FROM 4 TO 8 CARBONATOMS.